Biomedical subjects

Lars Frisén

Publications and source records attributed to Lars Frisén.

5 recordsLinked to original sources

PubMed2004

Vigabatrin-associated loss of vision: rarebit perimetry illuminates the dose-damage relationship.

PURPOSE: The utility of vigabatrin in the treatment of epilepsy is partially offset by its retinal toxicity. The relationship between dosage and damage is obscure. This may be due to perimetric shortcomings. The new technique of rarebit ('microdot') perimetry might be more informative. METHODS: Twelve patients who had been treated with vigabatrin for various durations were examined by manual, kinetic perimetry and by rarebit perimetry. RESULTS: Rarebit results differed significantly between patients and normal controls and rarebit deficits were directly proportional to cumulated vigabatrin doses (correlation coefficients were - 0.92 in the nasal field and - 0.82 in the temporal field). Manual perimetry results were less clearly related to dosage (r = - 0.54 and r = - 0.73, respectively). CONCLUSION: Rarebit perimetry indicates that each treated subject will develop visual loss and that visual loss will be proportional to the accumulated dose. Conventional perimetry is less well suited to detecting and quantifying vigabatrin-associated visual loss.

Adult↗

PubMed2004

Visual field of high-pass resolution perimetry in normal subjects.

PURPOSE: To investigate the properties of the visual field of high-pass resolution perimetry in normal subjects. METHODS: Four centers collected normative data for high-pass resolution perimetry. In two of the centers the subjects were stratified by age. One eye was tested per subject using high-pass resolution perimetry (Ophthimus). We tested 640 normal subjects and describe their visual field results by test location. We also analyzed the data by concentric zone, age, and by testing center. RESULTS: The individual test location averages confirmed a reduction in resolution with eccentricity. Resolution thresholds increased with age by 0.025 dB per year (P < 0.001). The mean ring size increased by about 1 dB from age 20 to 70. Among centers there were significant differences in the means and the change in threshold with age (P = 0.009). CONCLUSION: The normal visual field of high-pass resolution perimetry is characterized by an increase in threshold with eccentricity. We found significant differences among the centers that were likely due to multiple factors including differences in subject selection criteria. Whether such differences occur with other perimetric techniques is unknown.

Adult↗

PubMed2003

Subjective visual vertical and Romberg's test correlations in hydrocephalus.

OBJECTIVE: Exploration of the subjective visual vertical in pitch and Romberg's test in patients with hydrocephalus. Patients Eleven patients with communicating normal pressure hydrocephalus and six with non-communicating hydrocephalus due to aqueductal stenosis were examined before and after surgical treatment. METHODS: The subjective visual vertical was examined with a simple, custom-made articulated rod. The rod was faintly illuminated from within so as to appear floating in space when presented in darkness. The test task was to manually adjust the rod's position in pitch so that it appeared perfectly vertical. Romberg's test was performed under standardized conditions. RESULTS: Patients with a backward movement on Romberg's test showed a deviation of the subjective visual vertical, tilting the upper end of the rod closer to their eyes. Patients moving in other directions tilted the rod in the opposite direction (p < 0.01). The time in which the patients managed Romberg's test with open eyes correlated with the intratest variability of rod placement (r = 0.86, p < 0.001). After surgery, improvements on Romberg's test correlated with a decreased intratest variability of the subjective visual vertical. There were no differences between the two patient groups. CONCLUSIONS: Quantitative measurements of the subjective visual vertical in pitch correlate strongly with results of Romberg's test in patients with hydrocephalus.

Adult↗

PubMed2003

Characterization of vigabatrin-associated optic atrophy.

AIMS: To report the discovery of a previously unknown form of optic atrophy associated with use of the anti-epileptic drug vigabatrin. METHODS: We conducted a retrospective analysis of digitally enhanced ocular fundus photographs, kinetic visual field maps and treatment parameters for 25 patients, who were selected to represent a large spectrum of visual field defects. RESULTS: In all, 21 patients (84%) evidenced subtle, diffuse atrophy of the retinal nerve fibre layer, in a pattern accessible to scoring. Atrophy scores correlated with visual field remains and cumulative vigabatrin doses. A pathophysiological model is proposed that involves the lengths of intraocular (unmyelinated) retinal ganglion cell axons. CONCLUSION: Optic atrophy attests to the irreversible nature of vigabatrin's visual toxicity. Ocular fundus imaging should prove useful for objectively monitoring vigabatrin-treated subjects for visual toxicity.

Anticonvulsants↗

PubMed2002

New, sensitive window on abnormal spatial vision: rarebit probing.

Clinical tests have a poor sensitivity to low to moderate degrees of neuro-visual damage, possibly because their test targets involve numerous receptive fields. A new test used briefly exposed microdots of high contrast. Multiple visual field areas were probed repeatedly, with ever-new microdot positions. Normal subjects responded to a median 96.0% of probes. Patients with different visual field defects missed larger numbers of probes within defects and the deeper the defects, the larger the number of misses. Patients with minor chiasmal lesions averaged 1.8 times larger defects in microdot perimetry than in high-pass resolution perimetry, indicating superior sensitivity to minor damage.

Adult↗